In recent years, hospital Quality Improvement Collaboratives (QICs) have proliferated where groups of hospitals join together to share knowledge, benchmark performance, and work on common quality and safety improvement initiatives. While standardized data collection and sharing of comparative performance data are a common feature, they are insufficient for driving improvement in quality and safety. Additional components are needed to help hospitals examine their comparative data and initiate targeted improvement projects. Furthermore, there is little systematic understanding about which QIC components are effective in generating quality improvement and how to evaluate the success of these components. To address this empirical gap, we formed the Illinois Surgical Quality Improvement Collaborative (ISQIC) in 2014. ISQIC is a payer-funded QIC of 51 diverse Illinois hospitals focused on improving the quality and safety of surgical care. ISQIC is organized around mutual adoption of the widely-recognized American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) as a data platform and offers an enhanced QIC environment consisting of 21 components organized into five domains: guided implementation (e.g., mentors and coaches), education (e.g., formal curriculum), hospital- and surgeon-level comparative feedback (e.g., processes, outcomes, costs), annual local and statewide QI projects, and funding (e.g., overall program, pilot grants, bonuses). These components were designed based on evidence, detailed needs assessments, experiences from prior QICs, and interviews with QI experts. However, it is unknown how the components will need to be uniquely adapted for each hospital's local implementation and which components will effectively drive improvement. Thus, a generalizable model is needed for evaluating QICs. The overall aim of this study is to evaluate the effectiveness of a Quality Improvement Collaborative, such as ISQIC, in improving the quality of care. Our first aim is to conduct an iterative evaluatio of the adaptation and the implementation intensity of the ISQIC components by the hospitals. Our second aim is to assess changes in surgical quality (outcomes and processes of care) during the 3-year ISQIC implementation to quantitatively assess the effectiveness of a QIC. Our third aim is to explore the association between implementation intensity of the ISQIC components and improvement in quality. This proposal will be a public-private partnership in which implementation of ISQIC is supported by the payer, and this application will fund the evaluation of the implementation of the QIC. The research is significant because it provides detailed insights into how hospitals adapt and implement a QIC to improve quality, offers new knowledge by identifying the QIC components that are needed by hospitals to facilitate improvement beyond simply measuring outcomes, and addresses the broader need for generalizable models (e.g., tools and approaches) to evaluate how to improve development, implementation, and effectiveness of QICs.